The easiest way to write images to an SD card and USB drives with Chrome OS is to use the official Chromebook Recovery Utility. It can be used to create Chromebook Recovery media, and it will also accept .zip files containing images.
- Download the Chromebook Recovery Utility.
- Download the Raspbian .zip file.
- Launch the Recovery Utility
- Click on the Settings Gears icon in the upper right-hand corner, next to the window close icon.
- Select the Use Local Image option.
- Choose the .zip file you downloaded.
- Insert the SD card and click Continue.
- Read the warning and click the Create now button.
- Wait for the progress bar to complete twice (for unpacking and writing). This might take a few minutes. Once the process is complete, a big green checkmark will be shown.
- Close the program and eject the card.